U.S. patent number 5,059,327 [Application Number 07/089,180] was granted by the patent office on 1991-10-22 for cross-linked separation membrane and process for pervaporation.
This patent grant is currently assigned to Director-General, Agency of Industrial Science and Technology. Invention is credited to Shinsuke Takegami.
United States Patent |
5,059,327 |
Takegami |
October 22, 1991 |
Cross-linked separation membrane and process for pervaporation
Abstract
A preparation membrane for pervaporation which comprises a
crosslinked reaction mixture of a polyvinyl alcohol or polyvinyl
alcohol copolymer and a polystyrene sulfonic acid or polystyrene
sulfonic acid copolymer. A method for separating a mixture of water
and an organic compound by using the membrane is also
disclosed.
Inventors: |
Takegami; Shinsuke (Ohtsu,
JP) |
Assignee: |
Director-General, Agency of
Industrial Science and Technology (Tokyo, JP)
|
Family
ID: |
16384599 |
Appl.
No.: |
07/089,180 |
Filed: |
August 25, 1987 |
Foreign Application Priority Data
|
|
|
|
|
Aug 26, 1986 [JP] |
|
|
61-198044 |
|
Current U.S.
Class: |
210/500.34;
568/916; 159/DIG.27; 159/DIG.28; 203/14; 203/15; 203/16; 203/17;
203/18; 203/19; 210/500.42; 210/500.43; 210/640 |
Current CPC
Class: |
B01D
61/362 (20130101); B01D 71/76 (20130101); B01D
53/268 (20130101); Y10S 159/27 (20130101); Y10S
159/28 (20130101); B01D 71/28 (20130101); B01D
71/38 (20130101) |
Current International
Class: |
B01D
53/26 (20060101); B01D 61/36 (20060101); B01D
71/38 (20060101); B01D 71/28 (20060101); B01D
71/00 (20060101); B01D 003/00 (); B01D
013/00 () |
Field of
Search: |
;203/14-19,99,89,72,91,39,DIG.13,41 ;159/DIG.27,DIG.28,49
;210/500.42,640,638,500.43,500.34 ;568/916 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Bascomb, Jr.; Wilbur
Attorney, Agent or Firm: Wegner, Cantor, Mueller &
Player
Claims
What is claimed is:
1. A separation membrane for pervaporation which comprises an
intermolecular crosslinked reaction product of a mixture consisting
essentially of a polyvinyl alcohol or polyvinyl alcohol copolymer
and a polystyrene sulfonic acid or polystyrene sulfonic acid
copolymer.
2. A membrane according to claim 1, wherein the sulfonic acid in
the crosslinked reaction product is introduced in the form of a
sulfonate group.
3. A membrane according to claim 2, wherein the sulfonate is an
alkali metal sulfonate.
4. A membrane according to claim 1, wherein the membrane is
obtained by applying a mixture of polyvinyl alcohol and polystyrene
sulfonic acid on a porous supporting material and then subjecting
the mixture to a crosslinking treatment.
5. A membrane according to claim 4, wherein the mixing ratio of
polyvinyl alcohol and polystyrene sulfonic acid is in the range of
1.5 to 5.0 parts by weight of polyvinyl alcohol per 1 part by
weight of polystyrene sulfonic acid.
6. A membrane according to claim 4, wherein the crosslinking
treatment is effected by heating at 100.degree. to 150.degree.
C.
7. A membrane according to claim 4, wherein the porous supporting
material is an ultrafiltration membrane.
8. A membrane according to claim 4, wherein the porous supporting
material is made of polyacrylonitrile copolymer.
9. A method for separating a mixture of water and an organic
compound which comprises the steps of
(a) contacting one side of a separation membrane for pervaporation
comprising an intermolecular crosslinked reaction product of a
mixture consisting essentially of a polyvinyl alcohol or polyvinyl
alcohol copolymer and a polystyrene sulfonic acid or polystyrene
sulfonic acid copolymer with a liquid feed mixture containing water
and at least one organic compound; and
(b) withdrawing from the other side of said membrane a permeate in
a vapor state, said permeate containing water vapor in a
concentration higher than that in the feed mixture.
10. A method according to claim 9, wherein the organic compound is
an aliphatic alcohol.
11. A method according to claim 10, wherein the aliphatic alcohol
is ethanol.
12. A method according to claim 9, wherein the permeate contains at
least 80% by weight of water.
13. A method according to claim 9, wherein the sulfonic acid
contained in the crosslinked product is in the form of a
sulfonate.
14. A method according to claim 13, wherein the sulfonate is an
alkali metal sulfonate.
15. A membrane according to claim 7, wherein the porous supporting
material is made of polyacrylonitrile copolymer.
Description
FIELD OF THE INVENTION
The present invention relates to a separation membrane for
pervaporation. Further, the present invention relates to a method
for separating water from a liquid mixture of water and an organic
compound by pervaporation using the separation membrane.
BACKGROUND OF THE INVENTION
As a method for separating a liquid mixture of water and an organic
compound, a distillation method has been known for a long time.
However, it is very difficult to separate an azeotropic mixture, a
mixture of compounds having close boiling points, or a compound
which is liable to be denatured by distillation. Further, even if
compounds are separable by distillation, they often require a large
amount of energy. In order to solve these problems in a
distillation method, various separation methods using polymer
membranes have been studied. Among them, pervaporation is
considered to be useful for separation of a liquid mixture of water
and an organic compound. Pervaporation is a separation method
wherein a liquid mixture to be separated is fed to one side of a
polymer membrane, while the other side of the membrane is evacuated
or maintained at a reduced pressure to preferentially withdraw a
permeate in vapor form through the membrane.
The study of this method has been started in the 1950's and, for
example, pervaporation has been already disclosed in U.S. Pat. No.
2,953,502 to Binning. One characteristic of this pervaporation is
to make possible to separate, concentrate and purify an azeotropic
mixture, a mixture of compounds having close boiling points, a heat
decomposable mixture or the like which is difficult to treat by a
conventional distillation method. Another characteristic of
pervaporation is that it is not limited to a water soluble organic
liquid mixture as in reverse osmosis, but it is generally
applicable to a wide variety of organic liquid mixtures. Recently,
various studies of this method have been specifically made and
there are many reports relating to polymer membranes to be used in
the method.
For example, regarding separation of an aqueous ethanol solution,
U.S. Pat. No. 2,953,502 discloses a cellulose acetate homogeneous
membrane and U.S. Pat. No. 3,035,060 discloses a polyvinyl alcohol
membrane. However, both membranes have low separation factors.
Although Japanese Patent Kokai No. 59-109204 discloses a composite
membrane having a cellulose acetate membrane or a polyvinyl alcohol
membrane as a skin layer and Japanese Patent Kokai No. 59-55305
discloses a polyethylene imine crosslinked composite membrane,
their permeation rates or separation factors are low. In Japanese
Patent Kokai No. 60-129104, there is described a membrane
comprising an anionic polysaccharide. However, the material used
for the membrane described in the Examples of this literature is a
water soluble polymer and therefore durability of the membrane
against an aqueous solution containing a low concentration of an
organic compound is inferior. Then, in this literature, there is
also described that the membrane is subjected to a crosslinking
treatment with a sufficient amount of a crosslinking agent to
render the membrane essentially insoluble in water, although it is
not disclosed in the Examples thereof. However, usually, when a
crosslinking treatment is effected, a permeation rate is decreased,
while a separation factor is increased as shown by Comparative
Examples hereinafter. In German Patent No. 3220570, although there
is disclosed that a composite membrane obtained by coating a
polymer of polyvinyl alcohol crosslinked with maleic acid on a
polyacrylonitrile porous membrane shows very high separability, the
permeation rate thereof is very low.
When separation of an organic liquid mixture is carried out by
using these membranes, there are problems in practice as
follows.
That is, since separation efficiency is low, desired concentration
or separation can not be attained by permeation once through a
polymer membrane. Therefore, a multi-stage operation is required,
or it is necessary to combine pervaporation with another separation
method, which causes trouble in practice. Further, an amount of an
organic compound permeating through a polymer membrane (expressed
by the amount of the permeate per unit membrane area, unit membrane
thickness and unit time) is very small and, therefore, it is
necessary to make the membrane area much larger, or to extremely
thin the membrane thickness. In the former case, a larger apparatus
is required for industrial practice, which increases cost of
facilities. In the latter case, strength and durability of a
membrane are lowered, which causes trouble in practice.
In order to solve these problems, various attempt have been made,
but not yet been successful.
OBJECTS OF THE INVENTION
The present invention is to solve problems in separation of water
from a liquid mixture of water and an organic compound by
pervaporation, that is, such problems that both permeation rate and
separation factor can not be increased simultaneously in a
conventional separation membrane.
That is, one object of the present invention is to provide a
separation membrane for pervaporation having both high permeation
rate and high separation factor.
Another object of the present invention is to provide a method for
separating water from a liquid mixture of water and one or more
organic compounds.
These objects as well as other objects and advantages of the
present invention will become apparent to those skilled in the art
from the following description with reference to the accompanying
drawings.
BRIEF EXPLANATION OF DRAWINGS
FIG. 1 is an infrared absorption spectrum of one embodiment of a
separation membrane according to the present invention before
subjecting it to heat treatment for crosslinking.
FIG. 2 is an infrared absorption spectrum of the separation
membrane of FIG. 1 after subjecting it to heat treatment at
120.degree. C. for 2 hours to effect crosslinking.
SUMMARY OF THE INVENTION
The present inventor has studied intensively to obtain a separation
membrane for pervaporation which has both high separability and
high permeability, while maintaining good membrane forming ability
and high membrane strength. As the result, it has been found the
following separation membrane is suitable for this purpose.
Thus, according to the present invention, there is provided a
separation membrane for pervaporation which comprises a crosslinked
reaction mixture of a polyvinyl alcohol or polyvinyl alcohol
copolymer and a polystyrene sulfonic acid or polystyrene sulfonic
acid copolymer.
The present invention also provides a method for separating a
mixture of water and an organic compound which comprises the steps
of
(a) contacting one side of the separation membrane of the present
invention with a liquid feed mixture containing water and at least
one organic compound; and
(b) withdrawing from the other side of said membrane a permeate in
a vapor state, said permeate containing water in a concentration
higher than that in the feed mixture.
DETAILED DESCRIPTION OF THE INVENTION
The permeation rate used herein means the amount of a permeate per
unit membrane area per unit time and expressed by the unit of
kg/m.sup.2. hr. On the other hand, the separation factor (.alpha.)
is the ratio of the proportion of water to an organic compound in
the feed mixture, to that in the permeate in vapor form. That is,
.alpha.=(X/Y)p/(X/Y)f, wherein X and Y are compositions of water
and an organic compound in a two-component system, respectively:
and p and f represent the permeate and the feed mixture,
respectively.
In order to further illustrate the present invention in detail, a
mechanism of separation of liquid by pervaporation is set forth
hereinafter. That is, the mechanism of separation of liquid by
pervaporation is said to be dissolution and diffusion of liquid in
a membrane.
Generally, a separation factor .alpha..sub.AB which is a value
obtained by dividing a weight ratio of A component to B component
after permeation through a membrane by that before permeation can
be expressed by the product of a ratio of solubilities of A and B
components to the membrane and a ratio of diffusion rates of A and
B components in the membrane. Therefore, in order to increase the
separation factor .alpha..sub.AB, it is necessary to increase
either or both of the solubility ratio and the ratio of diffusion
rates of A and B components.
The solubility is mainly determined by interaction between permeate
molecules and a membrane (chemical miscibility). As a measure of
chemical miscibility between a material constituting a membrane and
a material to be separated, a solubility parameter is taken. Upon
choosing a material constituting a membrane, it is preferred to
choose a material having high chemical miscibility or similar
polarity to a material to be separated. And, it is said that, in
the case that a material to be separated (permeate molecules) is
hydrophilic, a material constituting a membrane having a high
solubility parameter and high polarity is suitable and, in the case
that a material is not hydrophilic, a material constituting a
membrane having reverse properties is suitable.
The diffusion rate is determined by shape, size and an
agglomeration state of permeate molecules, and a free volume of a
membrane. In order to increase a separation factor .alpha..sub.AB,
shape of permeate molecules in a feed mixture should be largely
different. In general, a smaller molecule has a larger diffusion
rate. However, when a given material to be separated is fixed, it
is difficult to increase a diffusion rate .alpha..sub.AB by
difference in shape of permeate molecules. On the other hand, a
free volume of a membrane is defined by molecular spacings in the
sense of a molecular measure, although it is not macroscopic holes.
When a low molecular weight material which makes molecular motion
of a high molecular weight material vigorous is contained, a free
volume of a membrane becomes larger, which facilitates permeation.
In a membrane having a larger free volume, difference between
diffusion rates due to difference in size of permeate molecules
becomes smaller, whereas, in a membrane having a smaller free
volume, difference between diffusion rates due to difference in
size of permeate molecules becomes larger. In order to increase a
separation factor by utilizing size of permeate molecules, a free
volume of a membrane should be small. In order to make a free
volume of a membrane smaller, there is employed such a method as
introduction of a crosslinking structure or crystalline structure
to form three dimensional network.
According to the present inventor's study on various membranes for
separation of an aqueous solution containing a water soluble
organic compound, particularly, ethanol by pervaporation, it has
been found that a separation membrane which is obtained by adding
polystyrene sulfonic acid to polyvinyl alcohol having a large
solubility parameter, i.e., strong hydrophilic nature, and
subjecting the mixture to heat treatment to effect intermolecular
crosslinking reaction between the hydroxy group of polyvinyl
alcohol and the sulfonic acid group of polystyrene sulfonic acid
can selectively separate the alcohol from the water-alcohol
mixture, and the membrane has sufficient durability as well as high
permeation rate and separation factor throughout a wide
concentration range of the alcohol. The sulfonic acid group of the
above reaction mixture may be introduced as a sulfonate group.
As the polyvinyl alcohol copolymer used in the present invention,
there can be used copolymers of polyvinyl alcohol and other
polymers such as polyethylene, polyvinyl acetate, polymethyl
acrylate, polystyrene, polyacrylonitrile, polyacrylic acid and the
like. However, in the present invention, preferably, polyvinyl
alcohol is used. As the polystyrene sulfonic acid copolymer, there
can be used copolymers of polystyrene sulfonic acid and other
polymers such as polyacrylonitrile, polyvinyl chloride, polymethyl
acrylate, polyacrylic acid and the like. However, in the present
invention, preferably, polystyrene sulfonic acid is used.
The separation membrane of the present invention can be prepared
by, for example, dissolving polyvinyl alcohol or the polyvinyl
alcohol copolymer, and polystyrene sulfonic acid or the polystyrene
sulfonic acid copolymer in water or an aqueous solution containing
a water soluble organic compound such as an alcohol or the like and
casting the solution on a porous supporting material, for example,
an ultrafiltration membrane. Drying and heat treatment are carried
out, simultaneously to effect intermolecular crosslinking to form a
coat layer on the porous supporting material a crosslinked reaction
mixture of the polyvinyl alcohol or polyvinyl alcohol copolymer and
the polystyrene sulfonic acid or polystyrene sulfonic acid
copolymer. The heat treatment is carried out at a temperature in
the range of 80.degree. to 200.degree. C., preferably, 100.degree.
to 150.degree. C. The mixing ratio of polyvinyl alcohol and
polystyrene sulfonic acid is in the range of, preferably, 1 to 10
parts by weight, more preferably, 1.5 to 5 parts by weight of
polyvinyl alcohol per 1 part by weight of polystyrene sulfonic
acid.
The porous supporting material that having micropores of several
tens to several thousands .ANG. on its surface. Examples thereof
include porous supporting material made of known materials such as
polysulfone, polyether sulfone, polyacrylonitrile, cellulose
esters, polycarbonate, polyvinylidene fluoride and the like. The
porous supporting material may be in any shape, for example, it may
be flat membrane, tubular membrane, hollow fiber membrane and the
like.
Preferably, the coat layer composed of the thin film of the
crosslinkable film is as thin as possible so far as it is pinhole
free. The thickness of the coat layer is 0.05 to 5 .mu.m ,
preferably, 0.1 to 1 .mu.m . In order to thin the thickness of the
coat layer, it is necessary to decrease the solids content of the
solution applied on the porous supporting material, or the
thickness of the coated film. The solids content is, preferably, 1
to 15% by weight, more preferably, 5 to 10% by weight. In order to
thin the thickness of the film, it is necessary to choose a
suitable coating method. In order to form a uniform pinhole free
film, the solution is preferably applied on the porous supporting
material with a bar coating machine, a spin coating machine and the
like.
In the membrane thus produced, OH group of polyvinyl alcohol and
SO.sub.3 H group of polystyrene sulfonic acid are reacted to form
intermolecular crosslinking. Formation of crosslinking can be
confirmed by solubility of the membrane in a mixture to be
separated or the infrared absorption spectrum of the membrane. When
crosslinking is not formed, the membrane is dissolved during
separation operation. A partially remaining sulfonic acid group is
neutralized with a base to convert into a sulfonate. Examples of
the counter cation of the sulfonate include alkali metals, alkaline
earth metals, transition metals and ammonium ions of the formula
R.sub.4 N.sup.+ wherein R is hydrogen or alkyl. Preferably, it is
an alkali metal, particularly, sodium.
The membrane thus formed is mainly used for separation of a mixture
of water and one or more organic compounds, for example, an aqueous
solution containing one or more organic compounds selected from the
group consisting of alcohols such as methanol, ethanol, 1-propanol,
2-propanol, n-butanol and the like; ketones such as acetone, methyl
ethyl ketone and the like; ethers such as tetrahydrofuran, dioxane
and the like organic acids such as formic acid, acetic acid and the
like aldehydes such as formaldehyde, acetaldehyde, propionaldehyde
and the like; and amines such as pyridine, picoline and the like.
Further, the membrane can be used for separation of a gaseous
mixture of water and these organic compounds.
According to the present invention, separation can be carried out
by the steps of
(a) contacting one side of the separation membrane of the present
invention with a liquid feed mixture containing water and at least
one organic compound; and
(b) withdrawing from the other side of said membrane a permeate in
a vapor state.
These operations per se can be carried out according to a known
method.
By using the membrane of the present invention, separation of an
organic liquid mixture throughout a wide concentration range can be
efficiently carried out at a large permeation rate with maintaining
a separation factor higher than that of a known separation method
using a conventional membrane. Thereby, a compact and rational
separation system can be realized and it is possible to improve the
ability of treatment and decrease in cost. Thus, according to the
present invention, a membrane separation method is practically
applicable for reducing operation steps and saving energy in
separation and purification processes in chemical industries.
The following Comparative Examples and Examples further illustrate
the present invention in detail but are not to be construed to
limit the scope thereof.
The Determination of Pervaporation
The following pervaporation experiments were carried out by
maintaining one side of a membrane to which a mixture of water and
a water soluble organic compound was fed at atmosphere pressure and
the other permeate side at reduced pressure not more than 0.3 mmHg.
The active surface of the membrane was directed to the feed side
and the feed mixture was added on the surface and stirred at a
constant temperature. At this time, effective membrane area was
15.2 cm.sup.2. Water and the organic compound permeated through the
membrane were collected by condensation with liquid nitrogen.
n-Propanol was added to the permeate as an internal standard and a
permeation rate and a separation factor were determined by TCD gas
chromatography. By the way, the separation factor of water to
ethanol .alpha..sub.EtOH.sup.H.sbsp.2.sup.O is defined as follows:
##EQU1## wherein X.sub.EtOH and X.sub.H.sbsb.2.sub.O are ethanol
and water contents (% by weight) in the feed mixture, respectively;
and Y.sub.EtOH and Y.sub.H.sbsb.2.sub.O are ethanol and water
contents (% by weight) in the permeate.
COMPARATIVE EXAMPLE 1
Polyvinyl alcohol having a polymerization degree of 2,000 (7 g) was
dissolved in water (93 g) at 80.degree. C. After cooling to room
temperature, the solution was applied on an ultrafiltration
membrane composed of polyacrylonitrile with a spin coating machine.
The coated ultrafiltration membrane was dried at 40.degree. C. for
1 hour and then subjected to heat treatment at 120.degree. C. for 2
hours. The pervaporation ability in aqueous 95% (w/w) ethanol
solution of the membrane thus obtained was such that the permeation
rate was 0.02 kg/m.sup.2. hr and the separation factor
(.alpha..sub.EtOH.sup.H.sbsp.2.sup.O) was 160.
COMPARATIVE EXAMPLE 2
Polystyrene having a polymerization degree of 1,000 to 1,400 (10 g)
was dissolved in carbon tetrachloride (200 ml) at 60.degree. C. for
1 hour. Then, the solution was placed in a four necked flask and
conc. sulfuric acid (30 ml) was added to the flask under nitrogen
atmosphere. The mixture was reacted at 60.degree. C. for 4 hours.
The reaction mixture was added to dehydrated ether to form a white
precipitate. To the precipitate was added carbon tetrachloride to
dissolve the precipitate. The solution was further added to
dehydrated ether to form a precipitate. This procedure was repeated
four times to purify the reaction product. The reaction product was
confirmed as polystyrene sulfonic acid by its infrared absorption
spectrum. To the polystyrene sulfonic acid thus obtained (1.2 g)
were added polyvinyl alcohol having a polymerization degree of
2,000 (1.8 g), ethanol (1.4 g) and water (24 g) and the mixture was
dissolved at 80.degree. C. The solution was applied on an
ultrafiltration membrane composed of polyacrylonitrile with a spin
coating machine (800 r.p.m.). The coated membrane was dried at
40.degree. C. for 1 hour and then subjected to heat treatment at
120.degree. C. for 2 hours to effect crosslinking. The
pervaporation ability in aqueous 95% (w/w) ethanol solution of the
membrane thus obtained was such that the permeation rate was
3.8.times.10.sup.-2 kg/m.sup.2. hr and the separation factor
(.alpha..sub.EtOH.sup.H.sbsp.2.sup.O) was 97.
EXAMPLE 1
Polystyrene having a polymerization degree of 1,000 to 1,400 (10 g)
was dissolved in carbon tetrachloride (200 ml) at 60.degree. C. for
1 hour. Then, the solution was placed in a four necked flask and
conc. sulfuric acid (30 ml) was added to the flask under nitrogen
atmosphere. The mixture was reacted at 60.degree. C. for 4 hours.
The reaction mixture was added to dehydrated ether and to form a
white precipitate. To the precipitate was added carbon
tetrachloride to dissolve the precipitate. The solution was further
added to dehydrated ether to form a precipitate. This procedure was
repeated four times to purify the reaction product. The reaction
product was confirmed as polystyrene sulfonic acid by its infrared
absorption spectrum. To the polystyrene sulfonic acid thus obtained
(1.2 g) were added polyvinyl alcohol having a polymerization degree
of 2,000 (1.8 g), ethanol (14 g) and water (24 g) and the mixture
was dissolved at 80.degree. C. The solution was applied on an
ultrafiltration membrane composed of polyacrylonitrile by a spin
coating machine (800 r.p.m.). The coated membrane was dried at
40.degree. C. for 1 hour and then subjected to heat treatment at
120.degree. C. for 2 hours to effect crosslinking.
The membrane was soaked in an aqueous ethanol solution for 1 hour,
aqueous 0.1 N NaOH solution for 1 hour, 0.1 N NaCl solution for 1
hour and then the ethanol solution for 1 hour and was dried at room
temperature.
The pervaporation ability of the membrane obtained is shown in
Table 1.
TABLE 1 ______________________________________ Separation Ethanol
Permeation factor Run conc. Temp. rate H.sub.2 O No. (wt %)
(.degree.C.) (kg/m.sup.2 .multidot. hr) (.alpha..sub.EtOH)
______________________________________ 1 90 60 0.34 1500 2 95 60
0.14 1430 3 99 60 0.03 990 4 95 75 0.23 950
______________________________________
EXAMPLE 2
Sodium poly-p-styrene sulfonate (10 g) was dissolved in water (100
ml). To the solution was added H.sup.+ type cation exchange resin
(Amberlite IR-120B) (25 ml) and the mixture was stirred for 1 hour.
By this procedure, the sodium poly-p-styrene sulfonate was
converted into poly-p-styrene sulfonic acid.
The ion exchange resin was filtered off and to the filtrate (50 ml)
were added polyvinyl alcohol (4.2 g) and water (50 g). The solution
was applied on a polyacrylonitrile ultrafiltration membrane by a
bar coating machine. The coated ultrafiltration membrane was dried
at 40.degree. C. for 1 hour and subjected to heat treatment at
120.degree. C. for 2 hours to effect intermolecular crosslinking.
The pervaporation ability of this membrane is shown in Table 2.
TABLE 2 ______________________________________ Separation Ethanol
Permeation factor Run conc. Temp. rate H.sub.2 O No. (wt %)
(.degree.C.) (kg/m.sup.2 .multidot. hr) (.alpha..sub.EtOH)
______________________________________ 5 50 60 40 26 6 75 60 0.25
49 7 95 60 0.03 500 8 95 40 0.23 1290 9 99 40 0.01 710
______________________________________
EXAMPLE 3
The membrane obtained in Comparative Example 1 was soaked in an
aqueous ethanol solution for 1 hour, 0.1 N KOH solution or 0.1 N
CsOH solution for 3 hours and then the ethanol solution for 1 hour
and was dried at room temperature. The pervaporation ability of
this membrane is shown in Table 3.
TABLE 3 ______________________________________ Separation Ethanol
Permeation factor Run conc. Temp. rate H.sub.2 O No. Base (wt %)
(.degree.C.) (kg/m.sup.2 .multidot. hr) (.alpha..sub.EtOH)
______________________________________ 10 KOH 95 60 0.16 840 11
CsOH 95 60 0.13 630 ______________________________________
EXAMPLE 4
According to the same manner as described in Example 1, a
separation membrane was prepared except that the mixing ratio
(weight ratio) of polyvinyl alcohol and polystyrene sulfonic acid,
and the total weight % (solids content) of polystyrene sulfonic
acid and polyvinyl alcohol were varied. The pervaporation ability
of the membrane prepared is shown in Table 4. The pervaporation
ability was determined by feeding aqueous 95% (w/w) ethanol
solution at 60.degree. C.
TABLE 4 ______________________________________ Separation Solids
Mixing* Permeation factor Run content ratio rate H.sub.2 O No. (wt
%) (wt ratio) (kg/m.sup.2 .multidot. hr) (.alpha..sub.EtOH)
______________________________________ 12 7.5 2.0/1.0 0.10 970 13
7.5 1.5/1.0 0.13 1070 14 7.5 1.0/1.0 0.13 360 15 5.0 1.5/1.0 0.10
190 16 3.7 1.5/1.0 0.11 140 ______________________________________
*polyvinyl alcohol/polystyrene sulfonic acid
EXAMPLE 5
To polystyrene sulfonic acid (1.2 g) were added polyvinyl alcohol
having a polymerization degree of (1.8 g), ethanol (14 g) and water
(24 g) and the mixture was dissolved at 80.degree. C. The solution
was applied on a glass plate and dried at 40.degree. C. for 1 hour
to prepare a membrane. The infrared absorption spectrum of this
membrane is shown in FIG. 1.
Further, the membrane was subjected to heat treatment at
120.degree. C. for 2 hours. The infrared absorption spectrum of
this membrane is shown in FIG. 2.
As shown by these drawings, absorption bands at 1180 cm.sup.-1 and
1450 cm.sup.-1 are newly appeared by heat treatment at 120.degree.
C. for 2 hours. These absorption bands are corresponding to
R--O--SO.sub.2 --R formed by the crosslinking reaction of the
polyvinyl alcohol and polystyrene sulfonic acid, and become more
intense by heating for a longer time.
* * * * *